This invention relates generally to timepiece calendar mechanisms, and more particularly to a twin jumper adapted to detent the movement of concentrically-arranged day and date indicating elements.
As used herein, the term "date ring" refers to a ring having numerals printed thereon in a circular array to indicate the monthly date (1 to 31). The term "day disc" refers to a disc having a circular array of letters or symbols thereon representing the days of the week (MON to SUN). In practice, the day-indicating element may be in ring form.
In one known type of calendar mechanism, a date ring is provided with a set of internal gear teeth, while a concentrically-disposed day disc is provided with a set of external gear teeth. The two sets of teeth are engaged by driven operating means which cause the date ring and the day disc to present date and day readings. In a mechanism of this known type, use is made of a jumper consisting of two resilient arms which merge at a pivotally-mounted hub, the arm extending outwardly from the hub at acute angles, whereby detents at the free ends of the arms engage the teeth of the day and date indicating elements.
A drawback of this prior arrangement resides in the difficulties experienced in assembly when placing the day disc in position. Because this disc covers the set of external gear teeth lying underneath it and the jumper arm associated with this set, which arm is under spring tension, the disc obstructs the entry of the detent of this arm into a gap between two gear teeth. In order, therefore, to facilitate assembly operations, it was heretofore the practice to provide a small window in the day disc giving access to a fine tool for lifting the resilient jumper arm during this critical phase of assembly.
This expedient is not satisfactory, for upon lifting one jumper arm to clear the gear teeth, the pressure then exerted by the other jumper arm is increased. As a consequence, the simultaneous actuation of the date ring and the day disc is seriously impaired.